Really depends on what your goal is with the rifle, what kind of rifle it is, and what kind of optic you have on it.

If the rifle already has some slope in the rail on the receiver, then a set of rings may work just fine. If it does not, then a one-piece mount such as the Desert Tech mounts we carry may be an advantage due to their integral slope.

It is also easier to find one-piece mounts that are the appropriate height for an AR than it is stand alone rings. Usually a minimum of 1.4" height is required, and sometimes heights beyond that are necessary for proper optic clearance or cheek weld.